All of the following are true except: select one:
a. the diastole is the relaxation phase of the heart beat where the pressure on the walls of the blood vessels is lowest.
b. the systole is the contraction phase of the heart beat where the pressure on the walls of the blood vessels is highest.
c. red blood cells are responsible for gas transport.
d. a centrifuged sample of blood would yield a composition of 45% plasma and 55% cells

d. A centrifuged sample of blood would yield a composition of 45% plasma and 55% cells

Explanation:

Blood is a mixture of plasma and formed elements. Plasma consists of the fluid portion of the blood and approximately makes up 55 percent of the blood. On the other hand, the formed elements are the red blood cells, white blood cells, and platelets which make up about 45 percent of blood.

organisms that lack symmetry are called asymmetrical and belong to phylum porifera/sponges.

organisms with specialized stinging cells belong to phylum cnidaria. stinging cells are called cnidoblast cells.

cnidarians show two morphological forms : polyp (sessile) and medusa (mobile)

filter feeding is observed in porifera members.  

alternation of generation is observed in coelenterata or cnidaria. there is alternation of asexual polyp form and sexual medusoid form. it is also referred as metagenesis.